Screw propeller



w. STANNUS SCREW PROPELLER Filed Feb. 20, 1930 2 Sheets-Shee yuvswron BY [zlr'lliam Siannua ATTO RN EYS Oct. 25, 1932. w. STANNUS 1,884,906

scRE w PROPELLER Filed Feb. 20, 1930 2 sheets- 5mm 2 INVEN'IOR Milli-am Efannufl ATTORNEY-S Patented Oct. 25 1932 UNITED. STATES.

PATENT O'FFlCE WILLIAM" s'm'm'ws, or DETROIT, MICHIGAN, ASSIGNOR 'rp srarmus rnorELmm oonrona'rrou, or person, mIonreAN, A oonromvrrou or women;

sonuw PROPELLER Application liled February 20, 1930. Serial No. 429,909. I

. The present invention relates to watercraft screw propellers having driving and dragging surfaces designed to eliminate characteristics tending to reduce propulsive capacity, formation of the blade being such that loss of efficiency because of radial divergence of water'due to centrifugal action is practically eliminated. In'other words, none of the rearwa-rdly-acting thrust of the propeller is lost through movement or displacement of water in any direction other than parallel to the propeller hub axis.

It may be said that no water is projected from the blade of my propeller in other than an approximately horizontal direction, loss of efficiency due to carrying water with the blades and radial projection therefrom at tips being eliminated. v

My invention is embodied in screw propeller blades of a radial thickness gradually decreasing from root to tip of blade, with working or. propelling-force faces formed by a slightly curved generatrix, the forward, or drag, faces being stream lined to reduce frictional resistance 'torotation while insuring suflicient strength to withstand deformation due to thrust stress.

Attainment of extremely high efiiciency is the chief object to be accomplished by thisinvention, which involves practical-application of the principles of stream-line design to propeller blades of a contour such that, beginning at about one-third of the blade length from axis, the effective propulsive area of the blade decreases as the distance.

from the axis increases, so that along equallyspaced concentrlc arcuate lines on the force faces of the blades, thepropulsive force exerted is uniform or, in other words,,the forcedistance ratio for about two-thirds of the blade length is practically constant. The

thrust on the water along any line at all points equidistant fromthe propeller axis is of practically unvarying value from leading totrailing edge of blade, stream lining of the.

.to the .pitch desired, all points equidistant from the propeller axis in a curved line traced on the force face of each blade by a point traveling at uniform rate in a path parallel to the propeller axis lie in the same plane set at Sitch angle to axis. f the accompanying drawings, wherein all reference figures have the same application and significance,

Flgure 1 is an elevation, or projection oh 9. plane at right anglesto the vertically disposed hub axis, showing how the propeller looks when viewed from the forward, or drag, side of the blades;

Fig. 2 is an elevation, or' projection on a plane parallel to the horizontally-disposed hub axis, showing how the propeller looks when viewingthe force face of one blade (upper) and drag side of the other (lower) blade. this view being at right angles to leading and trailing edges of the blades project beyond the forward and rearward faces of the hub;

Fig. 3 is an end view indicating the sweep of. the blades as seen when looking towards the tip of one blade and showing to whatextent both the leading and following edges thereof project beyond the forward and rearward faces of'the hub; v

Fig. 4 is a sectional view showing a. radial cross section from root to edge of one blade along line of Fig. 2, the edge of blade being rounded off, as indicated, on the forward or drag'side;

Fig. '5 is a cross-sectional view taken one line 5-5 nearthe root of the blade, where that shown in Fig. 1 and showing how both I the contour is such as tominimize mere u.

churning of the water, thereby making propeller more efficient; and

til

Figs. 6, 7, and 8 are blade sections taken on correspondingly numbered lines of Fig. 1 and showing the stream line contour of each blade, the thickness of which at any given point is considerably less than is characterlstie of ordinary propeller blades at corresponding points. These sectional views also give an idea of the variations in contour of the blades, as indicated by width from leading to trailing edges.

As herein illustratively disclosed by Figs. 1 and 2, my invention is embodied in a screw ropeller having but two opposed radial lilades, but it is equally ap licable to three and four-blade propellers, t 1e blades having curved and stream-lined leading and trailing edges 1 and 2, the tip of'blades being indicated by Figure 3 and hub by 4, the force face of blade by 5 and forward, or drag, side of blade by 6.

Being of uniform pitch, the force face 5 of each blade corresponds to that of a true screw, stream lining for reducing resistance to movement of the blade through the water as the propeller turns being confined to the forward, or dra side 6 of each blade, which, as indicated by ig. 4, is comparatively thin at the tip 3, the area of radial cross section or radial thickness ofblade increasing gradually from tip to root in proportion to the stress withstood, and from this maximum radial thickness the metal tapers away to both leading and following edges, 1 and 2, which are rounded off, as indicated by Figs. 6, 7, and 8, which are sectional views taken along the axial are 6, 7, and 8 of Fig. 1.

The force faces of the blades, are not radially straight, as would be the case if they corresponded to the line 'A-B of Fig. 4, but, as indicated, are of concave arcuate outline, departure from a straight radial line not only having a counteracting influenceon the diverging effect of centrifugal force developed by rotation of the propeller but serving also to reduce the torque requirement for.

a given boat speed.

The thick part of each blade follows an imaginary line roughly corresponding to the contour of the leading edge and running approximately parallel therewith at about onethird of the distance between the leading and following edges of the blade.

The accompanying illustrations show a propeller having hub and blades integrally cast, but my invention may equally well be embodied in blades cast separately from the hub and having at their inner ends suitable lugs for use in bolting them to a hub adapted to receive them.

What I claim is:

1. A watercraft propeller blade of unsymmetrical stream-line cross section, having its thickest portion disposed along an imaginary line directionally corresponding approximately to that of a line representing the leading-edge contour of the blade and located at about one third of the distancebetween the leading and following edges of blades, said .edges being of arcuate contour.

2. A watercraft propeller blade of unsymmetrical cross section, having a concave Working or force face surface and a convex drag surface, the latter being stream lined from root to tip along an imaginery maximumthickness line approximately paralleling the leading-edge contour, the area of blade from a position approximating one-third of the blade length from hub axis decreasing gradually towards curved tip of blade,'the edges of which are ofarcuate contour and rounded off on the drag side, substantially as shown and described.

3. A watercraft screw propeller having a series of radially arranged blades diagonally disposed with reference to the axis of the hub, said blades having concave working or forceface surfaces and convex drag-sidesurfaces, the latter being so stream lined as to produce an unsymmetrical disposition of the material of which the blade is made, the thickest part of each blade being located about one third of the widthof the blade from its leading edge and approximately parallel thereto from root to tip, the material tapering in both directions from the imaginary line of maximum blade thickness to the leading and following edges of said blades, said edges being rounded off on the drag side of each blade, and having a curvilinear contour such that as the distance from the axis increases the width of the blade correspondingly decreases so as to make possible the maintenance of an approximately uniform force-distance ratio on the outer two-thirds of the working surface of the blade.

4. A watercraft screw propeller having a plurality of radially-disposed blades of stream-line unsymmetrical cross section and of uniform true-screw pitch, of such contour, or outline, that the propulsive, or force-face, area of each blade decreases as the distance from the propeller axis increases, so that from the tip inwardly to a position approxi mately one-third of the length of blade away following an imaginary radially disposed line approximately parallel to the leading edge of blade at a distance therefrom equal to aboutone-third of the blade width, each blade having a contour such that the force-face, or

propulsive, area decreases as the distance from the axis increases, thereby equalizing distribution of propulsive .stress and making feasible the use of comparatively thin blades projecting beyond the fore and aft faces of propeller hub and tapering both Ways from the stream-lining point of maximum blade thickness. I

In testimony whereof I aflix my si ature.

WILLIAM STA US. 

